keep one's promise和keep one's words的区别

keep one's promise：遵守诺言；信守承诺；履行承诺 遵守诺言
keep one's promise/words：遵守某人的诺言
keep one's promise/appointment：信守承诺
所以两个词组应该没有什么不同,表达的意思差不多.个人觉得keep one's words显得没有keep one's promise正式,严肃.